This invention relates to a lubricating composition suitable for cold plastic working of aluminum alloys and a process for cold plastic working of aluminum alloys using the same.
Aluminum alloys are light-weight and have good appearance and quality, so that they are widely used as a variety of structural parts in domestic electrical equipments, articles for daily use, cars, communication apparatuses, optical devices, etc. These parts made by plastic working with high productivity. Particularly, cold working can be employed producing advantages in economical efficiency, dimensional accuracy, etc. Most of these worked parts are produced by drawing, ironing, stretching, extrusion, upsetting or the like process.
Heretofore, lubricants for working of aluminum alloys, there have been obtained by adding to a base oil such as a mineral oil, a synthetic oil, or the like an oiliness agent such as a fatty acid, a higher alcohol, or the like an extreme-pressure additive such as tricresyl phosphite, trilauryl phosphite, a chlorinated fat or oil, or the like or a solid lubricant such as graphite, molybdenum disulfide, or the like; or aqueous lubricating oil compositions obtained by adding water to the above-mentioned lubricating oil compositions. These lubricants are useful in rolling and drawing when the reduction of area is about 20% or less, but they are not suitable when the reduction of area becomes higher. Lubricants for ironing and stretching having larger plastic deformation (about 30% in reduction of area) and higher pressure and temperature at working surfaces, have been disclosed in Japanese patent unexamined publication No. 36303/79 where a lubricant is used which comprises a mineral oil, polyoxyalkylene alkyl ether diphosphate ester, a saturated or unsaturated fatty acid, a higher alcohol and a metallic soap.
A lubricating process for working a part with a still higher working ratio, has been proposed wherein a chemical film treated by hydrogen silicofluoride is formed on a surface to be worked, followed by formation of a film of metallic soap or solid lubricant and cold working. But such a process has as a problem the formation of the chemical film.
Prior art lubricants have the problems of that there occur linear scratch, peeling and cracks on the surfaces of products when the reduction of area becomes 35% or more, and the dimensional accuracy is lowered. On the other hand, when the surface to be worked is subjected to the chemical film treatment or metallic soap film treatment, the resistance to seizure is excellent, but the finish peculiar to aluminum cannot be obtained due to the gray treating which remains on the surface of product. Further, there are other disadvantages in that the treating steps become numerous, and it requires high costs and labor to control and handle the treating fluid and to dispose of the waste liquor.